Html5 和 Css3 - 水平导航栏问题

Question

我正在设计一个网页。我有两级导航，第一级的社交媒体按钮和后来的导航栏。我在获取导航栏的背景颜色以达到网页的完整长度时遇到问题，目前它随着导航栏开始和停止。我猜这是与位置或我的 clearfix 编码有关的问题？无论如何，我会很感激你的建议。我的代码如下，我附上了我网站的照片，以便您查看它的外观。

我的 HTML 代码：

<div id="wrapper">
  <header id="header" role="banner">
    <div id="logo">
      <a href="index.html"><img src="Images/title.png" alt="logo" width="1018" height="140"></a>
    </div>
    <div id="social">
      <ul>
        <li>
          <a href="https://twitter.com/SaveADHCNSW#" target="_blank"><img src="images/twitter.png" alt="Twitter" width="32" height="32"></a>
        </li>
        <li>
          <a href="https://www.facebook.com/Save-NSW-Government-Disability-
    Services-ADHC-709029659182219/" target="_blank"><img src="images/facebook.png" alt="Facebook" width="32" height="32"></a>
        </li>
        <li>
          <a href="https://www.youtube.com/channel/UCS0HQwz4LWWGS4AZhb5Ry3w" target="_blank"><img src="images/youtube.png" alt="Youtube" width="32" height="32"></a>
        </li>
      </ul>
    </div>
    <div id="clearfix">
    </div>
    <nav id="page_nav">
      <div class="menu">
        <ul id="navmenu">
          <li class="active"><a href="index.html">Home</a></li>
          <li><a href="aboutus.html">About Us</a></li>
          <li><a href="#">Get Involved</a><span class="darrow">&#9660;</span>
            <ul class="submenu">
              <li><a href="socialmedia.html">Social Media</a></li>
              <li><a href="unionmeeting.html">Union Meetings</a></li>
              <li><a href="rally.html">Rally</a></li>
            </ul>
          </li>
          <li><a href="#">News</a><span class="darrow">&#9660;</span>
            <ul class="submenu">
              <li><a href="shrewsnews.html">Shrew's News</a></li>
              <li><a href="update.html">Update</a></li>
            </ul>
          </li>
          <li><a href="gallery.html">Gallery</a></li>
          <li><a href="contacts.html">Contact Us</a></l>
        </ul>
      </div>
      <div id="clearfix">
      </div>
</div>
</nav>
</header>
</div>

我的 CSS：

* {
  margin: 0px;
  padding: 0px;
}

body {
  font-family: sans-serif;
  background-color: black;
}

#wrapper {
  width: 1366px;
  height: auto;
  background-color: black;
  margin: 0 auto;
  padding: 10px;
}

#header {
  width: 100%;
  height: 140px;
  background-color: black;
}

#logo {
  float: left;
  margin: 0px 0px 20px 50px;
  padding-left: 100px;
}

#social {
  float: right;
  top: 0px;
  margin: 0 auto;
}

#social ul li {
  float: left;
  list-style: none;
  padding: 5px;
}

#clearfix:after {
  display: block;
  clear: both;
}

#page_nav {
  background-color: #c50a13;
}

ul#navmenu {
  list-style-type: none;
  width: 800px;
  margin: auto auto 5px auto;
}

ul.submenu {
  list-style-type: none;
}

ul#navmenu li {
  outline: 1px solid white;
  width: 125px;
  text-align: center;
  position: relative;
  float: left;
  margin-right: 4px;
  color: #26b0f1;
}

ul#navmenu a {
  text-decoration: none;
  display: block;
  width: 125px;
  height: 25px;
  line-height: 25px;
  background-color: #c50a13;
  border: 1px solid white;
  border-radius: 5px;
  color: white;
}

ul#navmenu .submenu a {
  margin-top: 3px;
}

ul#navmenu li:hover > a {
  background-color: white;
  color: #c50a13;
}

ul#navmenu ul.submenu {
  display: none;
  position: absolute;
  top: 26px;
  left: 0px;
}

ul#navmenu li:hover .submenu {
  display: block;
}

.darrow {
  font-size: 14pts;
  position: absolute;
  top: 10px;
  right: 1px;
  color: dodgerblue;
}

Answer 1

更新：

你在 CSS clearfix 中忘记了一些东西。

#clearfix:after {
  display: block;
  clear: both;
  content: ''; /* add me */
}

此外，您的 HTML 中存在一些错误，这些错误可能会影响在不同浏览器中以不同方式呈现。

[1] <li> 的结束标签无效

[2] 在您的</nav> 结束之前额外添加</div>。

[3] 重复 ID：id="clearfix"

首先，修复重复的 ID。在你的 CSS 中，改变这个：

#clearfix:after {
  display: block;
  clear: both;
}

到这里：

.clearfix:after {
  display: block;
  clear: both;
}

这是您没有错误的 HTML。

<div id="wrapper">
  <header id="header" role="banner">
    <div id="logo">
      <a href="index.html"><img src="Images/title.png" alt="logo" width="1018" height="140"></a>
    </div>
    <div id="social">
      <ul>
        <li>
          <a href="https://twitter.com/SaveADHCNSW#" target="_blank"><img src="images/twitter.png" alt="Twitter" width="32" height="32"></a>
        </li>
        <li>
          <a href="https://www.facebook.com/Save-NSW-Government-Disability-Services-ADHC-709029659182219/" target="_blank"><img src="images/facebook.png" alt="Facebook" width="32" height="32"></a>
        </li>
        <li>
          <a href="https://www.youtube.com/channel/UCS0HQwz4LWWGS4AZhb5Ry3w" target="_blank"><img src="images/youtube.png" alt="Youtube" width="32" height="32"></a>
        </li>
      </ul>
    </div>
    <div class="clearfix">
    </div>
    <nav id="page_nav">
      <div class="menu">
        <ul id="navmenu">
          <li class="active"><a href="index.html">Home</a></li>
          <li><a href="aboutus.html">About Us</a></li>
          <li>
            <a href="#">Get Involved</a><span class="darrow">&#9660;</span>
            <ul class="submenu">
              <li><a href="socialmedia.html">Social Media</a></li>
              <li><a href="unionmeeting.html">Union Meetings</a></li>
              <li><a href="rally.html">Rally</a></li>
            </ul>
          </li>
          <li>
            <a href="#">News</a><span class="darrow">&#9660;</span>
            <ul class="submenu">
              <li><a href="shrewsnews.html">Shrew's News</a></li>
              <li><a href="update.html">Update</a></li>
            </ul>
          </li>
          <li><a href="gallery.html">Gallery</a></li>
          <li><a href="contacts.html">Contact Us</a></li>
        </ul>
      </div>
      <div class="clearfix">
      </div>
    </nav>
  </header>
</div>